Carbon fiber is widely used as a fiber for reinforcing a composite material in common industries such as those pertaining to automobiles, civil engineering and construction, pressure vessels, windmill blades and the like in addition to the sports and aerospace industries because it has high specific strength and specific elasticity compared to other fibers. Therefore, there is a strong need to increase the productivity of carbon fiber and improve the production stability of carbon fiber.
Polyacrylonitrile (PAN)-based carbon fiber, which is the most widely-used carbon fiber, is industrially produced by wet-spinning, dry-spinning or wet-dry-spinning a PAN-based polymer (precursor)-containing solution to obtain a precursor fiber, heating the precursor fiber under an oxidative atmosphere to convert the precursor fiber into a flame-retardant fiber and then heating the flame-retardant fiber under an inert atmosphere to carbonize the flame-retardant fiber to eventually form the carbon fiber.
The application range of such carbon fiber is becoming wider, and such carbon fiber is required to have high performance.
Therefore, various methods for preparing a high-performance carbon fiber have been actively researched. However, since a conventional precursor fiber for preparing a carbon fiber has a water content of about 4% or less, it is difficult to additionally stretch the precursor fiber to improve physical properties in a flame-retarding process, and thus it is difficult to improve the strength of the finally-produced carbon fiber.